This application relates generally to video signals and, more particularly, to combining video signals.
The popularity of television has generated a diverse array of programming in recent times. Viewers increasingly may access hundreds of channels devoted to a variety of subjects, resulting a highly competitive marketplace.
Programming increasingly may include value-added features, ostensibly to distinguish a channel from competing channels. Viewers may receive stock data simultaneously with a news program, for example. Many channels feature an identification logo which remain affixed on the display during the featured program. Sometimes a program is scaled down to occupy only a portion of the screen while emergency weather information, for example, is presented to the display.
Manufacturers of television displays, too, are offering value-added features which change the way programming is viewed. Picture-in-picture is a popular option which allows two programming channels to be viewed simultaneously. Programming guides are also available on many television sets.
Many of these value-added features involve personal computer (PC) graphics. PC graphics, typically created on a processor-based system, may be combined with a television signal prior to viewing on a television display. Alternatively, PC graphics data may be sent to a computer monitor for display.
The video signal that includes television programming is different from a PC graphics signal. In fact, graphics images are often created to be displayed on a computer monitor rather than on a television screen.
Computer monitors operate differently than television displays. While computer monitors may receive video data intended for a television, typically the video data is first converted prior to being sent to the computer monitor. Likewise, PC graphics data is typically converted prior to being transmitted to a television screen.
Mixing video and graphics signals together, likewise, typically requires one or both signals to be adjusted in some way. Color space conversion, progressive to interlaced conversion, and adjustment of data transmission rate, to name a few examples, may be performed on one or both signals prior to combining them.
A video and a graphics signal may be combined by buffering one signal, typically the signal moving at a faster rate, in a frame buffer memory. When a frame of graphics data is stored, for example, the frame buffer may be emptied at a slower clock rate, e.g., the rate of the slower video data. Once the faster data is slowed down the two signals may be combined.
However, frame buffer memory is expensive. A single frame of graphics data with an 800xc3x97600 resolution, at two bytes per pixel, fills a one megabyte frame buffer. Further, for real-time processing, the delay associated with filling the frame buffer may be undesirable.
Thus, there is a continuing need to combine video signals running at different clock rates in real time without excessive use of frame buffer memory.